The Beginning of Earth and Life
From radiometric dating (the rate of radioactive decay is constant over time), we know Earth has been here for about 4.56 billion years (in a universe 13.7 billion years old). According to the fossil record, life began about 800 million years later, or 3.8 billion years ago. This life was in the form of primitive single-cell microorganisms. It took more than 3 billion years before the first multi-cellular plants and animals appeared. That was about 670 million years ago.
About 520 million years ago the age of invertebrates and vertebrates began. This period lasted for about 320 million years. At the end of this age, which was about 3.6 billion years since the first single-cell microorganisms appeared, it yielded insects and the beginning of fish and reptiles. That took us to 200 million years ago, at which time the age of reptiles began and lasted for about 130 million years. This was the time of the dinosaurs. About 70 million years ago the first mammals appeared. This marked the beginning of the age of the mammals (hairy species that feed their young from mammary glands). It’s the age we are in now. We are but one of about 4,400 species of mammals.
Something very significant happened with the arrival of mammals: the beginning of nurturing behavior. Reptiles hatch from eggs. Although some reptiles tend their nest, most reptiles do not take care of their eggs. Young reptiles are able to feed and care for themselves. By contrast, mammals nurture their young for quite some time. Great emphasis is placed on feeding, protecting, and teaching skills to the young in order for them to survive on their own. Moreover, mammals possess the most highly developed brain of all animals. A large brain size in relation to their body and the brain structure known as the cerebral cortex provide mammals with highly developed intelligence and senses that increase their ability to learn and perform detailed tasks. So, 70 million years ago, we see the beginning of the shift from the reptilian brain to the more advanced brain.
Filed under: Earth and Life, cosmology
